Applicants have devised a method for treating waste drilling mud to reduce its volume and mass and to stabilize it in a sufficiently solid state that it is safe for disposal. Applicants' process involves fluctuating and separating the solid material from waste drilling mud, decanting off a portion of the water from the waste drilling mud as free water and then tabilizing the flocculated sludge, solids and remaining water in a sufficiently solid form that the material may be disposed of in an on-site pit or may be bagged for disposal in a land fill while meeting the applicable State and Federal requirements concerning disposal of waste material. Applicants' process is considerably more economical than present methods of disposing of waste drilling mud. Applicants' process reduces both the weight and volume of material which must be disposed of by separating a substantial quantity of the water base from the waste drilling mud.
The oil drilling industry produces large quantities of solids containing fluid waste materials as by-products of the drilling process. Included in these waste materials are a variety of aqueous base drilling fluid materials. These drilling fluids, or muds as they are known, have a variety of functions in the drilling process. For example, they cool, lubricate and clean the drill string and drill bit, they flush cuttings out of the bore hole, they line the bore hole to prevent structural collapse and seal the bore hole to prevent escape of pressurized gases which can be a hazard.
Muds, typically are suspensions of solid materials in water. The solid materials may be naturally occurring materials such as bentonite clays, attapulgite clays or other clay materials only with or without sulphonates, hydroxides or acids and other conditioning chemicals. Conditioning chemicals are used to influence or modify the properties of the mud. In use, particles or pieces of rock, and other drilling debris, may also be present in the mud. In some instances the mud may be a suspension of synthetic polymers or a combination of synthetic polymers with clays.
Applicants are aware of the following U.S. and Canadian patents, the disclosures of which are incorporated by reference herein:
______________________________________ 2,775,557 2,854,407 3,025,236 3,040,820 3,081,260 4,379,763 4,396,513 4,518,507 4,580,925 4,668,128 522,850 Canadian 522,851 Canadian ______________________________________
During the process of drilling, the composition of the drilling mud may require changing due to changes in the conditions in the bore hole or because the drilling mud has worn out and lost its effectiveness. When a change in the drilling mud occurs and the drilling mud is removed from the bore, it becomes a waste material and must be disposed of according to applicable State and Federal regulations. In the past, drilling mud was disposed of on-site in an earth pit. The water contained in the drilling mud percolated into the surrounding soil leaving a solid or semi-solid residue in the pit which could be covered with earth. The water base of the mud, including soluble chemicals, leached out into the surrounding water table, polluting the same. This method of disposal is no longer permitted. Waste water is not permitted to enter the surrounding water table.
At present, where State and Federal regulations permit waste pits at all, they must be lined with tough plastic sheet to prevent contaminated water from leaching into the surrounding water table. However, the plastic sheet may not always prevent the escape of water into the surrounding water table. Lined pits create another problem, however, as the waste mud is a colloidal suspension in water. If the pit is lined to prevent migration of water into the surrounding soil, the waste mud remains fluid and will not support burial under an earthen overburden. At many drilling sites, waste pits are not permitted and the waste drilling mud must be trucked away for subsequent disposal at a landfill. In either case, that is, where the drilling mud is to be disposed of on-site in a lined pit, or is to be trucked away, it is now necessary to treat the waste mud to solidify it. If the spent mud is not solidified, the covering earth will sink to the bottom of the pit and the spent mud will rise to the top.
The art has solidified waste drilling mud, both on-site and for trucking to off-site landfills, by filtration to increase the solids content, for example in a filter press, or by mixing in large quantities of cement and/or fly ash to produce a thick mass of material. A process of the latter type is disclosed in U.S. Pat. No. 4,668,128. The thickening and/or filtering processes have been only partially effective solutions to the problem of disposing of waste drilling mud. Filtration is expensive and the application of fly ash and/or cement to the waste drilling fluid increases its volume and its weight substantially. There is an approximate increase of 30-40% in the volume of the waste drilling mud and a 150-200% increase in the weight of the waste drilling mud when it is stabilized by an addition of fly ash and/or cement. This greatly increases the cost of off-site disposal of the drilling mud. The increased weight and volume increase the cost of trucking the waste material to an off-site landfill, and increases the landfill charges. Landfill charges are based on both volume and weight of the material disposed. Overall, closed systems (systems without on-site pits) have an increase in drilling costs of 20-30% over systems using on-site pits. This cost is generated in part by the increased cost of disposing of spent mud and in part by other consequences of using a closed mud system, such as reduced penetration rate and well bore instability.
Applicants' method of treating waste drilling mud has the advantage of reducing the volume and mass of the mud, rather than increasing it. Applicants' method also provides a stable, solidified mass, having a high solids content, suitable for disposal both on-site or in an off-site facility, such as a landfill. Applicants' invention in the first phase involves treating the disposed mud with a flocculating and dewatering material effective to settle the mud solids present in the waste mud. The mud solid particles agglomerate and precipitant leaving free water, which may be decanted from the settled mud solids and reused or disposed. Suitable water disposal is in a disposal well below the water table. In the event the foregoing does not overcome the problems of preparing a material suitably stabilized, for earth burial for example, the separated sludge of mud solids is to be further treated by a suitable water absorbing binder material as described hereinafter, leaving a sludge that is stabilized. The stabilized sludge can be buried on-site or removed to a suitable landfill at minimal cost.
The separated sludge, while being of much lower volume and weight than the initial waste fluid, may still contain only 20-50% solids by weight. Applicants have found that by using a suitable water absorbing binder material, the precipitated mud solids, or sludge, can be stabilized to a point that it may be buried on-site or removed to a suitable landfill at minimal cost. The stabilizing material does not increase the volume or weight of the stabilized solids to any significant degree, yet it is effective at maintaining the sludge in a stable, solid condition suitable for earth burial or other disposal without contaminating the surrounding environment.
Applicants' first phase is superficially analogous to methods of separating sewage solids and other solids containing waste water. However, dewatering drilling muds present a much more difficult task Drilling muds contain much higher solids than waste water. Typically, drilling muds contain from about 3 to 10% by volume and sometimes as high as 20% by volume or more, or about 7 to 22% by weight, typically, and in some cases up to 40% by weight or more. Moreover, the particular solids, i.e., colloidal clays and polymers, have a much greater affinity for water than normal waste water solids. In particular, clay mud solids are of colloidal size and the clay particles have a platelet shape. In aqueous suspension, each platelet has an electrical charge distribution over the platelet surface. Consequently, the platelets repel each other and resist attempts to agglomerate the clay into particles of sufficiently large size that they may be separated from the aqueous suspension by flocculation and dewatering. Also, these clay platelets attempt to align themselves in a position of minimum free energy setting up what is known as a gel structure. In addition, the clay matrix or lattice will hydrate, in suspension, to incorporate water into the matrix or lattice structure Conventional waste water treatment methods, if applied to drilling muds, may produce a flocculated suspension in which the water is even more tightly bound and which will not dewater on subsequent treatment.
Applicants' process uses two types of reagents to counteract the high affinity of the drilling mud solids for water and to separate the drilling mud from water and to prepare the separated mud to a stabilized disposable state. The initial flocculating or dewatering treatment utilizes a flocculant, preferably a polyelectrolyte flocculant similar to those normally used in sewage treatment, but of high molecular weight. The polyelectrolyte or flocculant is preferably of the synthetic type such as polyacrylamide flocculants or quaternary amine flocculants, or mixtures of both types. The flocculants chosen are those which carry ionizable groups which are effective to neutralize the charges on the suspended mud solids and to flocculate or coagulate the suspended solids from the mud suspension. On treatment, the suspended mud solids separate out from free water and precipitate as a wet sludge of mud solids. Applicants have found that polyacrylamide polyelectrolytes having molecular weights on the order of 10.sup.6 or 10.sup.7 and which carry a charge are particularly effective to precipitate the mud solids. Suitable compounds may be obtained from a variety of commercial sources including the Axchem Company, which sells suitable partially hydrolyzed polyacrylamide (PHPA) anionic electrolytes having a molecular weight of about 18.times.10.sup.6. Those products are commercially available, for example, under the trademark TELEZE, the products are designated by product numbers 158040, 158033 and 158021. For clay drilling mud suspensions, applicants have found that the high molecular weight PHPA electrolytes are those which are most effective to dewater the drilling mud compositions to separate the suspended material out as a sludge and to produce decantable free water from the drilling mud suspension.
Suitable quarternary amine polymers are those having a molecular weight of between about 10.sup.5 -10.sup.6 and having a charge of between about 60% and 85% per monomeric unit. These polymers are especially effective to agglomerate suspended clay platelets into larger particles which may be separated from suspension by flocculation. It is believed that the quarternary amine polymers are effective to neutralize the charge on the clay platelets and agglomerate the colloidal sized platelets into larger particles which may be separated or settled by flocculation. A particularly effective quarternary amine may be obtained from the Axchem Company under the trademark TELFIX, product number 158201. This material has an average molecular weight of about 150,000 and a charge of 77%. This material is a poly DADMAC (diallyl dimethyl ammonium chloride). Equivalent materials are available from other commercial sources.
In the next phase of applicants' invention, for stabilizing the separated sludge to a point at which it can be safely buried on-site or place on a landfill, applicants have found that water absorbing binders having the ability to absorb large amounts of water per weight of absorbent are effective to provide a stable sludge. The water absorbing material or binding material should preferably absorb or bind 50 and most preferably up to 100 or more times its weight of water. Suitable compounds may be chosen from water binding or gelling materials including organic stabilizing materials such as natural gums, e.g., carboxmethycellulose, guar, hydroxyethylcellulose, carrageenan, alginates and synthetic materials and mixtures of these materials. The natural materials may be most effective at treating fresh water muds and may be less effective on muds containing high salt concentrations or having high pH. Suitable effective synthetic materials include low molecular weight water absorbing polymers including low to moderate molecular weight polyacrylamide polymers. These synthetic polymers may have a molecular weight such that the polymer has a real specific gravity of about 1.14 and the dry particulate material will have a bulk specific gravity of about 0.85. The polymer has a melting point of between about 300.degree.-350.degree. F. The pH of a 0.5 percent solution of the polymer may vary from about 6 to 9, depending on the degree of substitution, if any, on the amine groups. The polymer may be cross-linked. Typical polyelectrolyte polymers will absorb up to one hundred times, or more, their dry weight of water and will retain this amount of water for over thirty minutes when subjected to one hundred psi pressure.
These polymers are commercially available from a variety of sources in dry particulate form and also as aqueous base solvent containing emulsions. Typical commercial emulsions have a pH of between about 6 and 8, a specific gravity of about 1.03, a boiling point of about 200.degree. F. and a flash point of about 210.degree. F. These emulsions typically have a Bingham plastic viscosity of about 30 centipoise and a Bingham yield point of about 18 (100 lb./ft.sup.2).
Inorganic colloidal materials may also be used, such as pyrogenic silica. These materials are all available from a variety of commercial sources, for example, the Cabot Corporation produces suitable pyrogenic colloidal silica under the trademarks CAB-O-SIL and CAB-O-SPERCE. Organic water absorbing gums and stabilizers are available from a wide variety of commercial sources. Particularly suitable polyacrylamide water absorbing and binding polymers are available from Worldwide Environmental Services, Inc., under the trademark WASTE-LOCK and designated by product numbers 1200, 2400, L1 and L24. It is preferred that these water binding materials be selected to have as high a water binding property as possible to reduce the expense of reagents and of transporting the stabilized material. Materials and mixtures having the characteristics of binding fifty times their weight of water, or more, are most effective and the most preferred compounds have the characteristic of binding up to one hundred times or more of their weight in water. The water absorbing binder will normally be added at levels of between about 0.5 to 2.0 pounds per barrel of treated drilling mud residue, or about 0.1 to 0.5% by weight. The amount may be increased or decreased, depending on the water absorbing capacity of the water absorbing binder used and on the degree of stabilization required in the treated mud residue. It will be appreciated that in some instances, for example, when the waste drilling mud has a sufficiently high solids content in its unseparated state, applicants' second phase treatment may be applied directly to the waste drilling mud. For example, by treating a pit of waste drilling mud to render it suitable for earthen burial. In such cases the water absorbing binder may be added at levels up to about 10% by weight or more of the stabilized residue.
It is thus an object of applicants' invention to provide a method of disposing of waste drilling mud.
It is a further object of applicants' invention to provide a method of separating solid materials from waste drilling mud to reduce the volume and weight of materials which must be disposed of.
It is an object of applicants' invention to provide a method of stabilizing waste drilling mud to avoid contamination of the environment.
It is thus an object of the present invention to find a method of disposing of waste drilling mud fluids that will not pollute the environment. It is a further object of the invention to provide appropriate materials for treating the drilling mud sludge and for obtaining a valuable sludge product.
It is an object of applicants' invention to provide a method of separating waste drilling mud solids from the water base of the drilling mud.
It is an object of applicants' invention to reduce the volume and weight of waste drilling mud, to permit economical disposal.
It is an object of applicants' invention to produce a stable waste drilling mud product that will support earthen burial.